Common air cushions for providing buffering and shock-absorbing functions (adapted to shoes, protective pads, etc.) are manufactured by two methods. One method is traditional, using two sheets sealed with heating and inflated with a gas for producing an inflated bed, a life belt or the like. Another method uses an extrusion blow molding process for producing three dimensional (3D) air cushions provided with a shape memorizing function and with recessed holes or recessed grooves in an upper surface to realize little transformation after inflation and maintain a basic 3D shape supporting structural function after deflation.
However, air cushions produced by the two kinds of methods mentioned above can not have completely smooth exterior surfaces. An air cushion produced by the former method has a swollen middle inflated portion surrounded by a sealed peripheral edge, and an air cushion produced by the latter method has recessed holes or recessed grooves. Thus, air cushions provided with substantially smooth surfaces can not be produced by these two methods.